In the processing of tubular knitted fabric, it is typical for the fabric to be wet processed at one or more stations, as in bleaching, dyeing, resinating and similar operations. The term "wet" processing, as used herein, refers to "foam" processing as well as to more conventional liquid processing. Because of the construction of knitted fabrics, wet tubular fabrics are extremely unstable, geometrically, and tend to become elongated and distorted during wet processing. Accordingly, the processing techniques for tubular knitted fabrics have conventionally included a final operation of spreading the dry fabric to width in the presence of steam, so that the final product has a desired width and geometric uniformity. At this stage, it is often necessary and desirable to perform certain additional adjustments on the fabric geometry, such as stripe straightening, in the case of fabrics having pronounced transverse stripe configurations.
In the wet processing of tubular knitted fabric, it typically has been necessary to perform finishing operations such as spreading to width, stripe straightening, etc. after the drying operation, depending somewhat on the character of the drying operation. In some instances, where a so-called Palmer-type dryer is employed, the fabric can be physically confined between a heated drum and a blanket, during the drying operation, such that the dried fabric being discharged from the dryer has a generally controlled geometry. However, dryers of this type are generally quite slow and have other disadvantages. More widely used are dryers in which the fabric is advanced on mesh-like drums or conveyors and relatively high velocity streams of air are passed through the fabric to remove moisture. Such dryers have many advantages in relation to speed and efficiency, but typically do not accommodate a high degree of control of fabric geometry, and post-drying finishing operations, such as spreading and steaming, stripe straightening, etc., typically are required.
In accordance with the present invention, a unique and extraordinarily effective method is provided for the drying of tubular knitted fabric, utilizing flowing streams of heated air, but under such conditions that the dried fabric emerging from the dryer unit is in substantially finished condition, of highly uniform width and geometry, substantially ready for the cutting table.
In accordance with one of the significant features of the invention, wet fabric delivered to the dryer is significantly but controllably overspread in terms of the ultimate width desired and, although the fabric is completely wet at that stage, it is nevertheless steamed as it enters the dryer. From that point, and throughout a substantial fraction of the path through the dryer, the fabric is carefully controlled and supported in terms of its geometry, so that the fabric remains as free as possible from tensions in any direction, particularly lengthwise, and unsupported traverses of the fabric are kept at an absolute minimum. The arrangement is such that, as the fabric traverses the drying system, although it loses some of the width imparted by overspreading at the entry, it loses such width in a highly controllable, uniform basis, resulting in fabric which, as discharged from the dryer, is of highly uniform width and cross line geometry, substantially ready for cutting. In a typical case, the fabric may in fact be calendered after drying, but primarily for "packaging" purposes, without significant width and/or stripe adjustment.
In the procedure of the invention, the starting material frequently (but not necessarily) is a heat settable tubular knitted fabric, rendered such either by reason of a poly/cotton construction in the first instance, or by reason of the addition of heat settable resins during wet processing. During the traverse of the drying system, the fabric becomes set and emerges from the discharge end of the dryer system as cured or set, finished fabric. With more conventional drying techniques (with perhaps the exception of the Palmer-type dryer, which has other disadvantages), it is usually necessary to dry without curing, because of the unsuitable geometry of the fabric as it reaches the discharge end of the dryer. This necessitates subsequent operations of calendering and stripe straightening, in conjunction with curing of the resin or setting of the polyester component, as the case may be.
In accordance with one aspect of the invention, the fabric, immediately or shortly preceding the drying operation, is wet processed and passed through an extractor nip, being discharged therefrom with a rather uniform moisture content typically ranging from about 60 to 100% moisture by weight of dry fabric for conventional wet processed fabrics, and around 25% for foam processed fabrics. In an in-line operation, the fabric travels directly from the wet processing stage to the entry spreader for the dryer system. More typically, since the line speeds of the wet processing equipment and the drying equipment may not be the same, and/or it may be desired to run more than one fabric string, the fabric may be discharged from the wet processing operation onto a truck or the like, from which it is later drawn into the dryer entry.
In another aspect of the invention, tubular knitted fabric may be directed into the new dryer system on an in-line basis from a mechanical compacting line operated on a wet basis. Heretofore, mechanical compressive shrinkage (compacting) of tubular knitted fabric for preshrinkage purposes has been performed on essentially dry fabric, which is steamed in advance of the processing nip. Compacting of the fabric in wet condition has, heretofore, been accomplished only with difficulty and expense, because of the problems involved in drying of the fabric subsequent to mechanical compacting, without loss of the compacting effect and geometry of the fabric. Where such practices have been carried out, typically it has required the use of a Palmer-type dryer with its attendant slow speed and other disadvantages. Pursuant to the present invention, wet compacted fabric may be discharged directly from the compactor into the entry of the dryer system and dried and set at economical speeds yet under a high degree of effective control, such that finished, compacted fabric emerges from the discharge side of the dryer.
The principles of the invention not only result in very significant economies in the finish processing of tubular knitted fabrics, but also achieve a more desirable product. Among the important advantages realized are that the fabric may be initially constructed with a somewhat looser stitch, which enables a higher yield of fabric to be achieved with a given weight of yarn.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments of the invention and to the accompanying drawings.